There are known continuous casting machines for steel strip, or similar products, wherein the crystallizer consists substantially of two crystallizer rollers, which are disposed between lateral containing walls and rotate in opposite directions to convey the liquid steel downwards and thus form the cast product.
In the V-shaped space which is created between the two crystallizer rollers, above the horizontal plane passing through their axes of rotation, the liquid steel arriving from a tundish forms a meniscus with a determinate height, which is controlled by means of suitable discharge means, for example of the immersion type or submerged entry nozzle (SEN).
In such continuous casting machines, one of the main problems to be solved is that of having a uniform initial solidification of the liquid steel inside the crystallizer, to create the so-called outer skin of the cast product, for which reason it is necessary to create conditions as equal as possible along the generatrixes of the rollers.
It is possible to ensure a uniform solidification of the liquid steel along the generatrix of the roller by integrating both a uniform distribution of the liquid steel along said generatrix and also a uniform temperature of the crystallizer along the same generatrix.
Until now, such controls have always been difficult and have not brought appreciable results, so that the above technical problem is practically unsolved in the present state of the art.
Document WO-A-93/19874 discloses a rotary roller for continuous casting, provided with longitudinal cooling conduits, parallel to each other and disposed in proximity with the periphery of the roller. The cooling conduits, inside the roller, are connected to each other in order to define a single coil fed by a single inlet conduit and a single outlet conduit, connected to the roller by means of a single rotary joint located laterally and coaxial to the roller. The coil of conduits is disposed so that there is an alternation in the direction of the flow of water between adjacent conduits, and the coil has a double linked spiral, so that the heat gradient on the periphery of the roller is uniform. The disadvantage of this roller is that the cooling water which enters at a relatively low temperature (for example 0° C.), exits from the roller at a relatively high temperature (more than 60° C.); in this way, the cooling conditions of the roller, along the generatrix of the roller in contact with the liquid steel where the first solidification occurs, are not uniform and therefore they can cause the formation of cracks in the cast strip.
Document EP-A-0873805 discloses a casting roller which comprises an inner cylindrical core and an outer tubular casing, forced through interference onto the inner core. Longitudinal conduits, parallel to each other, are provided both on the outer casing and on the inner core, to allow the cooling water to flow inside them and to cool the cylindrical surface of the roller. The conduits end in two circular chambers parallel to the front surfaces of the roller, so that the cooling water enters at one end of the roller and exits at the opposite end. It is also provided that several conduits can be grouped together and that the direction of flow of the water is inverted. The casting roller described in EP-A-0873805 has the same disadvantages as those described in WO-A-93/19874, because when the conduits are grouped together there is the same problem of a non-uniform cooling for the two adjacent conduits where the cooling water changes direction.
The present Applicant has devised, designed and embodied the device according to the invention to solve this technical problem fully and in a satisfactory manner.